1. Field of the Invention
This invention relates to a system for detecting and controlling positions of a mobile robot. More particularly, the invention relates to a system for detecting and controlling positions of a mobile robot, which can easily detect relative position and orientation within the workspace of the mobile robot. The invention also relates to a control system enabling a legged mobile robot to move stably and rapidly on stairs and in other such environments which restrict footfall position.
2. Description of the Prior Art
Mobile robots have been proposed in various forms including the wheeled, crawler and legged types. When such a robot carries out a task with respect to an object within its workspace (the work), it is required to orient itself with respect to the work for conducting the task. A mobile robot is, however, influenced by a number of unpredictable factors such as error in the measurement of its own position and slippage between the locomotion means and the ground surface occurring during movement. It is therefore not certain whether the robot will be properly oriented relative to the work when it completes its locomotion. When the mobile robot reaches its destination, therefore, it has to be able to ascertain its position and orientation relative to the work with high precision.
Ideally, the mobile robot would be able to continuously track its position relative to the work as it approaches the work. Since this would involve the processing of huge volumes of data, however, it is not practicable with currently available technology. For overcoming this problem, Japanese Laid-open Patent Application Nos. 59(1984)-32,009, 59(1984)-121,506 and 55(1980)-97,609 etc. teach methods for reducing the amount of processed data by laying auxiliary guide means (such as tape) along the locomotion paths within the robot operating space. The provision of buried electromagnetic induction wires has also been proposed.
These techniques are troublesome owing to the need to equip the workspace with special devices and, particularly in the case of subsurface wires, are quite costly to implement. In some environments, moreover, such as at a nuclear power facility, large-scale changes in the environment are not allowed.
Techniques have also been developed for enabling a mobile robot to discern its position and orientation relative to a work by pattern matching with camera images or other such visual information stored in memory beforehand. For reducing the amount of data that has to be processed, these methods generally use window processing to reduce search time. When the mobile robot's task is to inspect a piece of machinery, for example, the time for completing the task can indeed be shortened by having the robot ascertain its position using images taken of the pressure gauges and the like that are to be inspected. Since the mobile robot first identifies its position using other features of the equipment or the architectural environment and then searches for the work to be inspected, however, its working speed is slow. Although working speed can be speeded up by increasing the performance of the onboard computer, it is better for economical reasons to use a low-performance computer. In addition, autonomous robots are by nature subject to weight and energy consumption restrictions.
The present invention was accomplished in light of the foregoing circumstances and has as one of its objects to provide a system for detecting a position of a mobile robot and controlling the same which enables a mobile working robot equipped with a relatively low-performance computer to use a minimal number of landmarks provided in the workspace for detecting whether or not it has properly reached the work, accurately and in real time.
Moreover, among the various types of mobile robots, some types, such as the legged mobile robot, have discrete ground contact (footfall) positions. When such a mobile robot moves through an environment that restricts footfall position, as when it ascends or descends stairs, the footfall position has to be carefully controlled. As will be understood from FIG. 33, if a legged mobile robot's footfall position is too far back relative to a step during stair climbing, the resulting decrease in the ground contact area destabilizes the robot's attitude. If the footfall position is too far ahead, on the other hand, the foot strikes against the step riser when it moves up to the next step, again disturbing the robot's equilibrium. Thus when a legged robot goes up or down stairs or moves within some other such environment that restricts the footfall position, the robot's position relative to the environment (for example, stairs) has to be controlled.
In U.S. Pat. No. 5,402,050, a system is described for controlling a legged mobile robot enabling the legged mobile robot to move rapidly and with a stable attitude on stairs and in other such environments that restrict movement. Since this system uses contact sensors as the position detection means, however, it has low durability.
Another object of this invention is therefore to provide an improvement on the earlier system, more specifically to provide a system for detecting position of a mobile robot position and controlling the same which increases durability through the use of non-contact sensors and which achieves a further improvement in the robot's ability to ascertain its position.